466 THE AMERICAN MIDLAND NATURALIST 
The petals are either totally absent or represented by short linear 
appendages, and are usually, when present at all, of reduced number. 
In this case the three abortive stamens are reduced to small 
appendages or mere pimples. The disappearance of the regular 
number of stamens and petals is gradual, as in the other stemmed 
violets (e. g. V. canadensis and V. striata.) 
The presence of cleistogamous flowers in the Mnemion group 
in no’ way militates directly against the recognition of it as a 
separate genus, as there are other characters that prompted 
botanists as early as the very dawn of the science to consider 
Viola tricolor and its associates separate from Vzola odorata. 
Ruellius as early as 1542 gave this the name Pensea derived from 
the French Pensée whence the common name Pansy came. In 
fact since the cleistogamous flowers in this group when present 
come before rather than later as in the common violets, it shows 
that they are of a very different nature having the same character 
under entirely opposite ecological and physiological conditions 
In this sense this very identical characteristic is itself an indication 
of distinctiveness. 
BOOK NOTICE. 
“The Genus Phoradendron,”’ by William Trelease, Professor 
of Botany in the University -of Illinois, published by the Uni- 
versity early in June, is a royal octavo volume, containing 224 
pages and 245 plates, with a distribution map. 
This monograph of the exclusively American genus to which 
the mistletoe of the eastern United States belongs contains studies 
of morphology and geographic distribution, a complete reclassi- 
fication of these different plants, and descriptions of the 240 
species with their 37 varieties recognized as pertaining to the 
genus. The publication is based on a study of the materials pre- 
served in the great herbaria of the world, from which the descrip- 
tions are drawn, and is illustrated by half-tones from photographs 
of the types, printed on cameo paper, showing in natural size the 
essential characters of original specimens on which the species 
are founded. Nine-tenths of these are here figured for the first time. 
The work may be secured from the University of Illinois. 
Price, in paper, $2.00; cloth, $2.50 net. 
Pages 380-418, Vol. IV., published April 6, 1916. 
